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From: Florian Weimer <fweimer@redhat.com>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: libc-alpha@sourceware.org,  goldstein.w.n@gmail.com
Subject: Re: [PATCH v5 1/2] x86-64: Save APX and Tile registers in ld.so trampoline
Date: Thu, 15 Feb 2024 22:39:37 +0100	[thread overview]
Message-ID: <87bk8h8l0m.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <87le7l8lmy.fsf@oldenburg.str.redhat.com> (Florian Weimer's message of "Thu, 15 Feb 2024 22:26:13 +0100")

* Florian Weimer:

> * H. J. Lu:
>
>> Add APX registers to STATE_SAVE_MASK so that APX and Tile registers are
>> saved in ld.so trampoline.  This fixes BZ #31371.
>
> First APX is confusing?
>
> What's the impact on xsave_state_size and xsave_state_full_size?
> I'm worried that the loader trampoline now overflows small stacks.
> We used to have such problems in the past.

It adds 8,256 bytes on one AMX-capable machine.  This will impact
compatibility with existing software.  Stack usage is increased even if
the application does not use AMX at all.

I suggest to use a mechanism like STO_AARCH64_VARIANT_PCS to deal with
AMX, and only add the APX flag for now.

Thanks,
Florian


  reply	other threads:[~2024-02-15 21:39 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-02-15 20:32 [PATCH v5 0/2] x86: Update _dl_tlsdesc_dynamic to preserve caller-saved registers H.J. Lu
2024-02-15 20:32 ` [PATCH v5 1/2] x86-64: Save APX and Tile registers in ld.so trampoline H.J. Lu
2024-02-15 21:26   ` Florian Weimer
2024-02-15 21:39     ` Florian Weimer [this message]
2024-02-15 22:05       ` H.J. Lu
2024-02-15 20:32 ` [PATCH v5 2/2] x86: Update _dl_tlsdesc_dynamic to preserve caller-saved registers H.J. Lu

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